Rubber-based composition modifier, and vulcanizate and molded product of rubber composition containing the rubber-based composition modifier

A rubber-based composition modifier, comprising

• 100 parts by mass of a mixed rubber component containing 20 to 50 wt % of a chloroprene rubber and 50 to 80 wt % of an ethylene/α-olefin/unconjugated polyene copolymer,
• 20 to 60 parts by mass of magnesium oxide,
• 3 to 30 parts by mass of a softener, and
• 30 to 120 parts by mass of acetylene black, wherein:
• the mixed rubber component has a Mooney viscosity, as determined by the method specified in JIS K6300, of 60 to 180 at 100° C.;
• the magnesium oxide has a BET specific surface area, as determined by the one point method specified in JIS Z8830, of 20 to 150 m2/g;
• the softener contains at least one selected from the group consisting of oleic acid, linoleic acid, linolenic acid, pinolenic acid, castor oil, rape seed oil, soy bean oil, sesame oil, tall oil, coconut oil, palm oil, olive oil, corn oil, safflower oil, tung oil and rice oil;
• and
• the acetylene black has a nitrogen adsorption specific surface area (N2SA), as determined by the method specified in JIS K6217-2, of 50 to 160 m2/g.